Previous research has highlighted that while human listeners are capable of estimating the body size of dogs using the acoustic components of their growls, they also rate growls from larger dogs as more being aggressive than growls from smaller dogs. The aim of this study was to investigate the relative contributions of two cues to body size, fundamental frequency (F0) and formant frequency dispersion (Δf) to perceived levels of aggression. We found that participants that had just made an accurate assessment of caller size based on these characteristics then misattributed aggressiveness levels on the basis of these same size-related acoustic cues. More specifically, stimuli in which F0 and/or Δf were typical of larger dogs were rated as being more aggressive than stimuli typical of smaller dogs. Although both F0 and Δf influenced aggressiveness ratings independently, their interaction also had a significant affect. These results are discussed with respects to the human tendency to generalise reliable between-class acoustic cues to within-class stimuli and the resulting potential for making perceptual misattributions.